A monoclonal antibody to the NH2-terminal segment of human IFN-gamma selectively interferes with the antiproliferative activity of the lymphokine.

To gain more information about the relationship between the structure of IFN-gamma and its activity, a peptide corresponding to a hydrophilic peak between amino acids 4 and 16 was used to immunize mice and generate mAb. mAb IGMB-15 reacts to both native and rIFN-gamma and neutralizes the antiproliferative activity of IFN-gamma without affecting its antiviral activity or its ability to up-regulate HLA-DR Ag expression. Moreover, we observed that mAb IGMB-15 was unable to inhibit the binding of radiolabeled IFN-gamma to its cellular receptor. These findings show that the NH2-terminal region may somehow be involved in the biologic activity of IFN-gamma. Besides, the capability of mAb IGMB-15 to inhibit the antiproliferative but not the antiviral activity of IFN-gamma in the same cell (HEp-2) suggests the presence of different elements involved in signal transduction, which may account for the multiple activities of the lymphokine.

Natural human antibodies to gamma interferon interfere with the immunomodulating activity of the lymphokine.

Natural antibodies to gamma interferon (IFN-gamma) were found in patients suffering from different viral diseases and, at a lower titer, in healthy individuals. Such antibodies were affinity-purified and studied for their capability to interfere in vitro with the antiviral and immunomodulating activity of IFN-gamma. Data obtained show that these human anti-IFN-gamma antibodies have no inhibitory effect on the antiviral activity of IFN-gamma. On the contrary, they are able to inhibit the expression of Fc receptor sites and HLA-DR antigens induced by IFN-gamma on the U-937 cells, a human monocytoid/macrophage-derived cell line. These antibodies can also interfere in a mixed lymphocyte culture (MLC) with the proliferation of lymphocytes and the generation of cytotoxic lymphocytes. However, they showed only a moderate inhibitory effect on the cytotoxicity generated in MLC to K-562 cells. Human antibodies capable of interfering with the immunomodulating activities of IFN-gamma might open up a new field in clinical therapy for those diseases that carry evidence of activated cell-mediated immunity.

Inhibition of the biological activity of human interferon-gamma by antipeptide antibodies.

To study the domain(s) responsible for the different biological activities of human interferon-gamma (HuIFN-gamma), rabbits were immunized with peptides corresponding to the five most hydrophilic amino acid sequences of the lymphokine. The resulting antisera were able to recognize both the immunizing peptide and the native protein. Antibodies to the carboxy-terminal region (amino acids 125-137) of HuIFN-gamma were able to interfere with the immunomodulating, antiviral, and antiproliferative activities of the lymphokine. Inhibition of the antiproliferative and antiviral activity was also observed using antibodies raised against the amino-terminal region (amino acids 4-16) and amino acids 80-95, respectively, but to a lesser extent than that observed with antibodies to the carboxyl terminus. The capability of these antibody preparations to partially interfere with only one of the lymphokine's biological activities might be explained by a mechanism of steric hindrance. The use of polyclonal antibodies allowed us to limit the presence of epitopes responsible for recombinant (r)HuIFN-gamma biological activities to the carboxy-terminal region.

Purification of natural human IFN-gamma antibodies.

Natural antibodies to interferon gamma (IFN-gamma) were found in patients suffering from various viral infections, but also at weak titers in healthy individuals. In the present study we describe a one-step chromatographic procedure for the purification of the anti-IFN-gamma antibodies from human Ig preparations, using a recombinant IFN-gamma-coupled Sepharose CL4B affinity column. The antibodies to IFN-gamma were eluted from the column using 3 different methods without loss of immunological activity. They were found to be Ig, mostly of the IgG1 subclass, and, in the biological assay, to be able to neutralize the de novo expression of Fc receptor sites induced by IFN-gamma on U937 cells.